The long-term goal will be to obtain a systematic and detailed understanding of basal forebrain anatomy. Specific attempts will be made to define the intrinsic and extrinsic relations of the ventral striato-pallidal system. During the present project period, this will include: examining the collateralization of ventral pallidum and nucleus accumbens projections and attempting to identify the transmitters that are used in these prejections. These first questions will be studied using fluorescent retrograde tracers combined with transmitter specific immunofluorescence. Studies will also proceed on the synaptic relations of ventral straiatum and pallidum by the use of combined light-electron microscopic techniques. These will include Golgi-EM alone, or in combination with retrograde tracing, anterograde tracing, and EM immunocytochemistry. Thus, this second group of experiments will allow examination of the dendritic and local axonal arborization of individual neurons, and identification of the source of their extrinsic synapses, as well as their projection targets. In addition, the transmitters used by projection neurons and by synapses contacting these neurons may also be identified. The basal forebrain figures prominently in many theories that attempt to identify the biological substrate for neurological and mental disorders. The basic anatomical information that will result from our experiments will be essential in the formulaton of realistic theories of basal forebrain function that will be so necessary in this new era of metabolic brain imaging.